1. Field of the Invention
The present invention relates to a cutter head, and particularly to a cutter head for a civil construction machine, such as a shield machine, a tunnel boring machine, a pipe-jacking drive shield machine, a casing drill and a roadheader, for excavating a tunnel, a pile hole, a caisson hole and the like.
2. Description of the Related Art
In a nowadays boring machine used in a civil construction for excavating a deep hole or a tunnel having a circular cross section or the like, the cutter head of the machine is usually driven by a motor through a transmission shaft in order to carry out a single-direction rotary cutting on the soil over the entire cross section of the cutter head. However, such an arrangement involves several problems.
First, the machine body must be capable of resisting the reaction transmitted thereto from the soil through the cutting head during the cutting operation in order to prevent the machine body from rotating, bouncing or even being spoiled. In addition, since the cutter head rotates in a single direction about its axis of rotation, for example, in the clockwise direction as viewed toward the advancing direction of the cutter head, the excavated tunnel or hole inevitably gradually deviates from the predetermined route toward the right.
The solutions to the aforementioned problems have been none other than to increase the size and/or the weight of the machine in order to sustain the reaction produced during the cutting operation and to reduce the normal pressure exerted on the soil by the cutter head and/or decrease the rotating speed of the cutter head in order to minimize the deviation of the excavated tunnel or hole from the predetermined route.
However, while by taking the above measures it may be possible to solve the aforementioned prior art problems to a certain degree, the cost is increased due to the larger size and heavier weight of the machine and the cutting efficiency is lowered due to the smaller normal pressure exerted by the cutter head and the smaller rotating speed of the cutter head.
Moreover, with a conventional cutter head, since a single-direction rotary cutting over the entire cross section of the cutter head is performed on the soil, when the cutter head encounters a large single stone or the like, it is more often than not that the large single stone is inlaid onto and hence carried by the cutting head for rotation. Consequently, the cutter head stops advancing for excavating and the large stone carried by and rotating with the cutter head severely damages the soil surface previously cut.